1. Field of the Invention
The present invention relates to exposure apparatuses and exposure methods, and device manufacturing methods, and more particularly to an exposure apparatus and an exposure method used in a lithography process to manufacture electron devices (microdevices), and a device manufacturing method using the exposure apparatus and the exposure method.
2. Description of the Background Art
Conventionally, in a lithography process to manufacture electron devices (microdevices) such as a semiconductor device (an integrated circuit and the like), a liquid crystal display device and the like, a projection exposure apparatus (a so-called stepper) employing a step-and-repeat method, or a projection exposure apparatus (so-called scanning stepper (also called a scanner)) employing a step-and-scan method is mainly used.
In this type of exposure apparatus, in general, a position of a wafer stage which moves two-dimensionally while holding a substrate such as a wafer or a glass plate and the like on which a pattern is transferred (or formed) (hereinafter collectively called a wafer) was measured, using a laser interferometer. However, due to finer patterns accompanying higher integration of semiconductor devices in recent years, requirements for position control performance of a wafer stage with higher accuracy have increased, and as a consequence, it has become difficult to ignore short-term variation of measurement values caused by temperature change of the atmosphere on the beam path of a laser interferometer, and/or air fluctuation which occurs due to the influence of temperature gradient.
To improve such inconveniences, various proposals have been made of inventions related to exposure apparatuses that employ an encoder having a measurement resolution of the same level or higher than a laser interferometer as a position measurement device of a wafer stage (for example, refer to U.S. Patent Application Publication No. 2008/0088843). However, in the liquid immersion exposure apparatus disclosed in U.S. Patent Application Publication No. 2008/0088843 and the like, the wafer stage (gratings provided on the upper surface of the wafer stage) may be deformed influenced by heat of vaporization and the like due to the influence of the liquid evaporating, and there still was room for improvement.
To improve such inconveniences, the inventor has previously proposed an exposure apparatus that is equipped with an encoder system which irradiates a measurement beam on a grating provided on a rear surface of a table holding a wafer from a head section provided on the tip of a measurement arm consisting of a cantilever (for example, refer to, U.S. Patent Application Publication No. 2010/0073652, and U.S. Patent Application Publication No. 2010/0073653).
However, according to further studies, in the encoder system using the measurement arm described above, it became clear that the influence of background vibration including floor vibration and the like was large in a band of around 100 Hz to 400 Hz. Especially, with the wafer size increasing, the size of a wafer table on which the wafer is mounted also will increase, and for example, on a wafer table on which a wafer in the near future having a diameter of 450 mm is mounted, the length of the measurement arm used for position measurement will become 500 mm or more, and it is expected that vibration of the arm tip from which the measurement beam is to be emitted can no longer be ignored.
However, with more and more finer semiconductor devices, requirements for position control accuracy of the wafer has gradually become tighter, and now the maximum value of a permissible position error is about 1 nm. When such an accuracy is required, even in the encoder systems disclosed in U.S. Patent Application Publication No. 2010/0073652, U.S. Patent Application Publication No. 2010/0073653 and the like described above, a measurement error at a level that cannot be ignored may occur due to temporal drift of the grating pitch of the grating.